Composite pressure vessels are often fabricated as cylindrical tubes with hemispherical end caps. During the fabrication process, the filaments of graphite or glass are wound in a continuous pattern including both the cylindrical portion and the end caps. For materials and structures testing purposes, a cylindrical tube is an ideal specimen to represent the cylindrical portion of the vessel. For example, a composite cylindrical tube can be fabricated by either filament winding or tape wrapping techniques to have the same lay-ups angle as a cylindrical portion of a pressure vessel. The cylindrical tubes so fabricated will have the same mechanical properties as the cylindrical portion of the pressure vessel. The tube, however, can be fabricated at a small fraction of the cost of a pressure vessel with integral end caps.
A problem associated with realistic pressure testing of cylindrical specimens is that the tube ends must be sealed in such a manner that the tube does not leak, that there are no induced bending stresses at the interface between the tube and the end cap, and that the axial load of the internal pressure is carried by the cylindrical walls of the tube. In typical designs, a metal flange with an insert is utilized to bond the tube specimen using adhesive. The adhesive is under shear stress when the tube is internally pressurized. The shear strength of the adhesive depends upon the type of adhesive used, the bonding procedure, the material for the adherent, and the cure operation. However, regardless of how careful the bonding operation is conducted, the failure of a cylindrical composite tube under internal pressure often occurs at the end fitting of the tube interface. These and other disadvantages are solved or reduced using the invention.